1. Field of the Invention
This invention relates to the removal of volatile organic contaminants from water, and in particular to the stripping/desorption from water and catalytic oxidation of such volatile organics in the gaseous phase.
Wastewater effluent from chemical or petrochemical plants often contains volatile organic compounds (VOCs). Many of the VOCs are known to be toxic and hazardous. To meet increasingly tougher environmental standards, the wastewater must be treated to remove the pollutants before being discharged.
2. Description of the Prior Art
Currently, carbon adsorption and air stripping are the most commonly used VOC removal techniques. The treatment consists of two steps: 1) removal of VOCs from the wastewater by air stripping and 2) destruction of VOCs contained in the resulting air stream by catalytic oxidation. While the air stripping is a simple and reliable operation for the removal of VOCs from water, the oxidation of VOCs in the humid air stream into harmless compounds (CO.sub.2 and H.sub.2 O) on a conventional oxidation catalyst is inefficient because the catalyst must be heated to high temperatures to avoid deactivation by the moisture. In this case, the equipment and energy costs can be prohibitive.
An alternative method is to contact the contaminated wastewater with oxygen or air in a conventional trickle-bed reactor packed with oxidation catalysts (Three-Phase Catalytic Reactors--Gordon and Breads Science Publishers, Ramachandran, P. A. et al., 1983). This allows the oxidation of pollutants to occur in the liquid phase. Unfortunately oxygen is only sparsely dissolved in water. As a result, the rate of oxidation is low because the process is often limited by mass transfer of reactants to the catalyst sites.
Applicant has previously developed a hydrophobic oxidation catalyst containing a noble metal (Pt, Pd, Rh, Ru, or Ir) and combinations thereof, on a hydrophobic support e.g. styrene divinyl benzene co-polymer, fluorinated carbon and silicalite. See U.S. Pat. No. 5,009,872.